TH72011

433MHz

FSK Transmitter

Page 4 of 21

REVISION 012 - JUNE 14, 2017

3901072011

1. Theory of Operation

1.1. General

As depicted in Fig.1, the TH72011 transmitter consists of a fully integrated voltage-controlled oscillator (VCO), a

divide-by-32 divider (div32), a phase-frequency detector (PFD) and a charge pump (CP). An internal loop filter

determines the dynamic behavior of the PLL and suppresses reference spurious signals. A Colpitts crystal oscillator

(XOSC) is used as the reference oscillator of a phase-locked loop (PLL) synthesizer. The VCO’s output signal feeds the

used either to directly drive a loop antenna or to be matched to a 50Ohm load. Bandgap biasing ensures stable

operation of the IC at a power supply range of 1.95 V to 5.5 V

1.2. Block Diagram

Fig. 1: Block diagram with external components

2. Functional Description

2.1. Crystal Oscillator

A Colpitts crystal oscillator with integrated functional capacitors is used as the reference oscillator for the PLL

synthesizer. The equivalent input capacitance CRO offered by the crystal oscillator input pin ROI is about 18pF. The

crystal oscillator is provided with an amplitude control loop in order to have a very stable frequency over the specified

supply voltage and temperature range in combination with a short start-up time.

CX1

FSKDTA

antenna

matching

network

VEE

XOSC

low

voltage

detector

PA

XBUF

VCO

PLL

CP

PFD

32

OUT

PSEL

RPS

FSKSW

ROI

XTAL

CX2

8

1

7

5

3

2

mode

control

ENTX

4

6

VCC